If the nth term of an A.P. is 4n + 1, then the common difference is

1, 1,  3/4  ,1/2,5/16,.........................,

0, 11, 26, 45,               .

80, 75, 65, 50,               .

4, 9, 20, 43, 90,               .

f(6, 4) equals to

1W  2V  3U  5T  ?  13R

HV  GT FR EP DN    ?

I  M  Q ?

258  130  66  ?  18  10